I have a client with a three phase supply & want to connect a single phase inverter with change over switch.
I have attached a wiring diagram of what I would like to do.
I have a client with a three phase supply & want to connect a single phase inverter with change over switch.
I have attached a wiring diagram of what I would like to do.
Last edited by Tonye; 11-Feb-19 at 05:42 PM.
Hi
Without knowing the size of the incoming supply and the size of the inverter - In theory I don't see a problem with your drawing besides the other odds and ends that need to accompany alternative supply , indicator lights, charge circuit etc .
In practice I would not do it and would prefer to install separate DB with the inverter circuits that are going to be used .
SANS 10142 - 7.12.2.4 does not allow you to switch off circuits manually so the cost to install extra relays etc to drop the load to match the inverter is going to come to the same time and cost as creating a separate DB .You also run the risk that somebody forgets about the inverter and connects a 3 phase piece of equipment up.
The risk is to high to do wahat you are wanting to do , In my opinion.
7.12.2.4 Where the alternative supply is intended to provide a supply to an
installation that is not connected to the main supply, or to provide a supply
as a switched alternative to the main supply, the capacity and operating
characteristics of the alternative supply shall be such that danger or damage
to equipment does not arise after the connection or disconnection of any
intended load as a result of the deviation of the voltage or frequency from the
standard range. Means shall be provided to automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
alternative supply is exceeded
Thanks for this GCE.
I am aware of indicator lights, charge circuits, notices etc..
This is for a std residential property & all loads are single phase. There is no 3phase outlets or other 3phase connections on the premises.
One question is, would the 3phase E/leakage still function when supplied with single phase.
I have done a similar installation where a sub DB was installed with it's own single phase E/leakage
However it was relatively easy to move the circuits over due to the flush design of the DB.
On this installation the DB is raised & would prove difficult to move the circuits.
I am also trying to minimise costs.
After speaking to a few colleagues, there seems to be a debate on whether the Neutral on the 3 phase connection should also go through the changeover switch.
See attached
http://www.prellexpower.co.za/files/...0phase_new.pdf
The layout will look something like this.
http://www.prellexpower.co.za/images/basic%20layout.jpg
Hi Tonye
I would agree that the neutral goes through the change over . I assume that the Change over switch is rated to the Eskom supply
I still feel that you will be breaking the regulations by exceeding the inverter capabilities and the cost savings you are trying to achieve are going to come back to bite later.
My interpretation of this regulation is the following.Originally Posted by GCE
That danger or damage to equipment does not arise after the connection or disconnection of any
intended load as a result of the deviation of the voltage or frequency from the
standard range.
And
Means shall be provided to automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
alternative supply is exceeded
I think what they are saying here is that there needs to be overload protection for the alternate power supply
and not automatically disconnecting of individual circuits
The Changeover switch is 63A 4pole, adequate for Eskom supply
Last edited by Tonye; 18-Feb-19 at 11:10 AM.
This is not about taking grey area short cuts, minimum regulation standards, or my own standards.
This is about finding affordable solutions for clients which meet all regulation standards and my standards.
I understand when it comes to large commercial installations, high load equipment is automatically disconnected when running off an inadequate alternate power source, as Joe Soap would probably not even know where to turn off said equipment.
However this is a residential property.
There are no individual loads which will exceed the capacity of the alternate power supply.
However a combination of loads would.
Scenario with Eskom power on. The total load of the installation trips the main breaker. Which circuits or appliances does Joe soap turn off.
Even with a sub Db the total load could exceed the alternate supply capacity & again which circuits does Joe soap turn off.
My client (not Joe Soap) has a gas hob & is looking at installing a gas geyser to make provision for longer power outages.
He is aware that untill he installs a gas geyser that he would need to turn the geyser breaker off when changing over to alternate power
to avoid unnecessary tripping.
The system I am installing will be adequate to feed the other circuits, provided the total load does not exceed the alternate power supply capacity.
Should the total load exceed the capacity, which circuits should be automatically disconnected?
Here is the irony, Our national grid (Eskom) which supposedly provides 40MW does not have the capacity (Load Shedding)to supply the installation but the alternate supply must.
The cost to move circuits to a sub DB which still doesn't guarantee tripping due to the total load, or to make provision to automatically disconnect certain loads in a residential DB (which normally do not have the space for automatic disconnecting devices), or installing an unaffordable inverter battery system to cope with the whole installation just doesn't make sense.
So he has to get up to changeover to alternate power but is not allowed to turn off his geyser
prior the changeover (this has to happen automatically)
What faults?
Am I missing something here?
Last edited by Tonye; 18-Feb-19 at 09:33 PM.
Hi
Eskom Load shedding - automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
supply is exceeded
If you install a sub DB with circuits that will be fed from the inverter, that will be within the current rating (eg light circuit or two , router, TV,DSTV etc ) you do not need to install a change over switch and when the Eskom supply drops away the change to alternative supply will be seamless .
If you are going to put in extra circuits that may exceed the load of the inverter than install a loadshed mointoring device that can drop circuits automatically .
Generally you design an installation and then stipulate the supply to the main incoming or sub DB based on the loading calculations as per SANS 10142-1 clause 5.3
5.3 Basic provisions
5.3.1 Estimated load
The load of an installation shall be estimated to determine the type and
capacity of the required electricity supply.
NOTE 1 Annex C gives an example of estimating the load for residential installations
but the method is not to be regarded as an exact method.
NOTE 2 The supplier may have special requirements for large installations and for
installations that need special consideration.
On Domestic single phase supplies that are running close to tripping you would install a load shed relay between a stove and geyser for example to prevent nuisance tripping.
Experience has taught me that the client never does what he says he is going to do.
The regulations ask us to estimate the load and then specify the supply.
Unfortunately with inverters it is a money story and the client only wants to spend X amount. Then we need to make sure the load does not exceed the inverter and automatically disconnects load if the capacity is going to be exceeded.
To me the regulations are pretty clear.
No where do I find in the regulations that I may manually disconnect load if the client does not have money to pay for automatic disconnection.Maybe I am reading incorrectly.
Morning All
I have a comment about automatic changeovers.
The regulations clearly state that in a three phase installation all phases and neutral shall be switched with regards to alternative supplies I have yet to see any automatic changeovers do this.
Hi SeanM, you are correct with regards neutral being switched.
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